A fuel cell is a power generator, which converts chemical energy stored within fuels and oxidants directly into electrical energy through reactions of its electrodes. The types of fuel cells are diverse and their classifications vary. According to the properties of their electrolytes, fuel cells can be divided into five types including alkaline fuel cells, phosphoric acid fuel cells, proton exchange membrane fuel cells, fused carbonate fuel cells, and solid oxide fuel cells. Wherein, a proton exchange membrane fuel cell includes a so-called direct methanol fuel cell (DMFC), which directly uses methanol as fuels without modifying the same into hydrogen gas. This is also at present a technique that can generate relatively high power. Such fuel cells may be applied to large power plants, vehicular power generators, portable power supplies, and so forth.
It is essential to control the concentration of liquid fuels while commercializing such types of fuel cells as DMFC. Theoretically, fuels with lower concentrations produce less electricity, and fuels with higher concentrations produce more electricity. Accordingly, to maintain the concentration at a predetermined level, a concentration detector is needed to monitor the concentration of liquid fuels in real-time. As such, the electrical output of fuel cells can be regulated, and electronic products using the cells will not be damaged due to unsteady power supplied by the fuel cells.